feat(audio): add waveform preview playback

[flamboh]

Summary

• add a SoundCloud-style waveform preview to the selected-track editor
• support play/pause, elapsed/duration, pointer drag seeking, keyboard seeking, and horizontal panning
• stop/reset before paint on selection replacement or whenever the editor becomes inaccessible
• pause when Settings opens, mobile Back returns to the library, or the sidebar sheet covers the editor
• degrade safely when playback or waveform construction is unavailable

Resource and lifecycle safety

• serialize waveform decoding to one AudioContext
• reject compressed files over 96 MiB
• require finite positive duration and enforce a conservative 256 MiB decoded-PCM estimate before decoding
• retain an exact post-decode PCM gate as defense in depth
• use source generations so stale decode/media events cannot populate a replacement, including same-ID/new-File updates
• skip canceled queued work, discard canceled in-flight results, close contexts, and revoke object URLs
• document Web Audio's non-cancelable decodeAudioData behavior accurately

Verification

• vp check
• bun run typecheck
• bun run test (428 tests on the mobile-navigation base)
• bun run build
• two fresh implementation reviews plus repeated rechecks after lifecycle fixes

Dependency

Targets #125 (codex/mobile-workspace-navigation) because preview visibility must follow the mobile page/sheet accessibility state.

Manual follow-up

The Playwright spec was not executed because project instructions say not to start a development server during manual-review workflows.

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 2535bb9.}

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	tagium	2535bb9	Commit Preview URL Branch Preview URL	Jul 23 2026, 04:56 AM

[flamboh]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(audio): add waveform preview playback #127 👈 (View in Graphite)
• feat(ui): add mobile workspace navigation #125
• feat(export): confirm bulk downloads #123
• feat(metadata): reopen cleanup suggestions #121
• feat(ui): polish workspace states #120
• feat(metadata): add advanced editor #124
• feat(metadata): add advanced field policy #122
• refactor(audio): make formats explicit #119
• main

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